In an input/output process device for controlling input/output devices, the present invention relates to an input/output system capable of designating the input/output devices by a plurality of addresses.
It is a general trend in recent large scale general-purpose electric computer systems that addressing to input/output devices is made by hardware. For example, where one input/output device is connected to a plurality of input/output channels through a plurality of input/output control devices, a program only designates the input/output device as the object of access but does not designate a route reaching that input/output device (i.e. the input/output channels and the input/output control devices). In such a computer system, the hardware grasps the connection state of the input/output devices and selects the route reaching the input/output device designated from the program on the basis of its management information. An input/output processing architecture of this kind is disclosed in, for example, "IBM System 370/Extended Architecture, Principles of Operations, SA22-7085" on IBM. To select the route, the hardware keeps the information on the input/output control device group to which the input/output device is connected and the information on the input/output channels to which each input/output control device is connected, for each input/output device.
In the architecture described in the reference mentioned above, only one device address of the input/output device used on an I/O interface is defined for the input/output device. Therefore, all the input/output control devices to which the input/output device is connected have the same control device address.
For the reason described above, if a plurality of input/output control devices are connected to one channel, the input/output control devices having the same controller address must be eliminated. If the input/output control device is connected commonly to two or more computer systems, each computer system must allot the same address to this input/output control device. Thus, flexibility of system architecture drops.
It is a first object of the present invention to allot mutually different addresses to a plurality of input/output control devices connected to a common input/output device.
It is a second object of the present invention to make it possible to determine an input/output device address for input/output control devices used commonly for a plurality of computer systems without limitation of address setting in each of the computer systems.